U.S. Pat. No. 4,672,501 entitled "Circuit Breaker and Protective Relay Unit" describes the use of a digital circuit interrupter employing a microprocessor in combination with ROM and RAM memory elements to provide both relaying as well as protection function to an electrical distribution system. The current transformers used for monitoring the circuit current are also connected to provide operating power to the microprocessor and related circuit components. In the event that the circuit becomes interrupted upon the occurrence of a fault condition, it is difficult to determine the magnitude as well as the cause of the overcurrent condition that initiated the fault since the digital circuit interrupter loses operational power.
U.S. Pat. Nos. 4,428,022 and 4,751,606 each describe means for automatically converting from system power to an auxiliary power source as soon as the electrical distribution circuit is interrupted.
U.S. Pat. Nos. 5,089,928 and 5,220,479 describe connecting an internal battery to the display so that the trip information is readable after the circuit interrupter operates to disconnect the protected circuit from the electrical distribution system.
When the circuits are intentionally disconnected for test purposes as well as to repair associated electrical equipment, the auxiliary power source, usually a battery, becomes drained in the process. Later when called upon to provide auxiliary power in an actual overcurrent condition, there is the possibility that the battery may not then have sufficient remaining charge to power-up the digital circuit components.
It would be beneficial to provide a system for controllably using the auxiliary power source solely when there is an actual overcurrent condition and to conserve battery power for such occurrence.